1. Field of the Invention
The invention relates to high refractive index photo-patternable organic and organometallic sol-gel precursors and the methods by which they are prepared. The invention further relates to sol-gel compositions and polymers derived from sol-gel precursors. The materials described herein are useful in various optical waveguide applications.
2. Description of the Related Art
Advances in fiber-optics and integrated optics have been made to address the rapidly growing need for high-bandwidth transmission of information, particularly for telecommunications. Needs, however, are still growing, placing additional demands on increasing rates of transmission as well as processing, switching, and routing of optical signals.
Particularly, future demands on transmission and processing will likely require bandwidth needs of greater than 100 GHz. The current transmission infrastructure relies upon modulators that are based on lithium niobate, and bandwidth is currently limited to 10 GHz. Additionally, lithium niobate is difficult to grow because it is a crystal and is also difficult to integrate into an optical circuit. See Dalton, L., “Nonlinear Optical Polymeric Materials: From Chromophore Design to Commercial Applications,” Advances in Polymer Science, Vol. 158, pp. 1-86 (2001). Modulators based on organic and/or organometallic materials might overcome these deficiencies.
Desirable features of optical modulators include low insertion loss, high signal modulation efficiency, and durability under the conditions imposed by processing and operation. An example of a device structure upon which organic modulators are built is the Mach-Zehnder modulator. This modulator is a multi-layer device comprised of substrates, electrodes, cladding, and waveguide layers.
Recently, particular attention has been given to the materials required for cladding and waveguide layers. Desirably, these materials would have (1) low optical transmission losses (<1 dB/cm) in the realm of telecommunications wavelengths (1300-1600 nm), (2) high-conductivity to increased poling efficiency, (3) compatibility with various substrates, such as glass and quartz, (4) refractive indexes greater than 1.40, (5) good chemical and thermal stability, and (6) UV-visible light patternability. Sol-gel chemistry using organosilicones has been investigated. See Hench, et al., “The Sol-Gel Process,” Chem. Rev. 1990, 90, 33-72.
U.S. Pat. No. 6,391,515 to Su et al., the contents of which are hereby incorporated by reference, describes a process by which sol-gel optical waveguides are manufactured. U.S. Pat. No. 6,054,253 to Fardad et al., the contents of which are hereby incorporated by reference, discloses a photo-lithographic process by which ridge waveguides are made. However, neither of these references contains a disclosure as to the manufacture of low optical loss, high refractive index waveguides for the telecommunication wavelength range of 1300-1600 nm. U.S. Pat. No. 6,908,723 to Fardad et al., the contents of which are hereby incorporated by reference, discloses photo-patternable sol-gels having a refractive index of about 1.50 at 1550 nm by introducing C—F bonds along with a metal refractive index adjuster, preferably titanium, to a sol-gel. However, the maximum refractive index disclosed by Fardad et al. was only about 1.50. Furthermore, the reference describes methods that use metal oxides other than silicon oxide to obtain patterned sol-gel materials, such as Ti—O bonds and Zr—O bonds.
JP 2005-290312 to Matsumoto et al. lists a phenyl derivative of a bis-substituted dialkoxysilane. However, the compositions described by Matsumoto et al. are unrelated to optical waveguides. Furthermore, Matsumoto et al. fail to describe a synthesis for the bis-substituted dialkoxysilane. Oshita et al., “Convenient synthesis of alkoxyhalosilanes from hydrosilanes,” J. Organometallic Chem. 689 (2004) 3258, reports the preparation of phenyldialkoxysilanes using PdCl2. However, the catalyst described by Oshita et al. only works with aromatics having certain substitution patterns, and will not effect transformation on arylsilanes with ortho substitution. Corey, et al., Organometallic Chem. 304 (1986) 93-105, discloses rhodium catalyzed dehydrogenative coupling of alcohols to silanes via chloro(tris-triphenylphosphine)rhodium(I). However, Corey et al. do not disclose a controlled addition using methanol and ethanol with the resulting products containing a Si—H bond. The only chemistry done under a controlled addition was with tert-butyl alcohol, which results in a more stabile structure that can survive harsher conditions, due to the enhanced steric inhibition of the larger tert-butyl group to chemistry involving the silicon center. This enhanced steric inhibition significantly reduces the reactivity of the Si—H in further transformations, possibly affecting the choice of catalysts that could be used.
European Patent Appl. Pub. No. 0277023 to Kouji, et al. describes the hydrosilylation of allyl methacrylate to a trialkoxysilane using H2PtCl6. WO 2005/103062 to Eilenstine et al. discloses a method of hydrosilylating trialkoxysilanes to terminal olefins using a rhodium catalyst, but at an elevated temperature unsuitable for the functional groups present. However, there remains a need for improved sol-gel compositions having low optical loss coupled with high refractive index values and methods of making thereof.